Bipolar electrolytic cell



June 24,1969 J CQLMAN BIPOLAR ELECTROLYTIC CELL Sheet Filed Aug. 31. 1966 Joau E. COL M M INVENTOR. BY w 3% June 24, 1969 J. ,E. COLMAN BIPOLAR ELECTROLYTIC CELL Sheet of 2 Filed Aug. 31. 1966 United States Patent US. Cl. 204-268 11 Claims This invention relates to bipolar electrolytic cells for use in electrolytic processes which require an electrolysis zone where most of the electrolytic reactions take place, and an auxiliary zone where little if any electrolysis takes place, between which zones good electrolyte circulation is desirable. More particularly, this invention relates to bipolar electrolytic cells especially suited to the production of halates, perhalates, or hypohalites of alkali metals, especially chlorates, e.g., sodium chlorate. In these latter electrolytic reactions, the auxiliary zone is known as the reaction zone, within which certain chemical reactions, which are not electrolytic in nature, take place.

Taking as an example the production of chlorate, the principal desired reactions taking place in the electrolysis zone are as follows:

Anodic Undesirable side reactions which may take place on the anode within the electrolysis zone are as follows:

In the reaction zone the following essential reaction takes place:

Small gas bubbles of hydrogen (H are evolved at the cathodic surface in the electrolysis zone and tend to rise, entraining the electrolyte as they do so.

It has been common practice in the past to produce alkali metal chlorates electrolytically by means of a bipolar electrolytic cell positioned in a large container or tank. A typical prior art bipolar electrolytic cell for this purpose consists of a housing in the form of an opentopped box in which a large number of spaced, parallel electrodes, usually of graphite, is positioned. Electrical connections are made to two or more, but not to all, of the electrodes for the purpose of supplying electrical energy to the cell. In eifect, the electrodes are connected in series electrically through the electrolyte in the cell. At the top and bottom of the housing on boh sides thereof are tubes leading into the housing. These tubes constitute inlet (lower) and outlet (upper) tubes and are provided in suflicient number to communicate with each one of the spaces between pairs of adjacent electrodes. Each pair of adjacent electrodes and the intervening space between them constitute a unit cell. The housing is supported above the floor of the container or tank, and the latter is filled with electrolyte.

The electrolyte enters each unit cell through the lower tubes, these being below the level of the electrolyte in the tank, is electrolysed in the unit cells, and the electrolysed solution is discharged to the tank via the upper tubes, the tank constituting a common reservoir for all unit cells. In many cases, circulation of the electrolyte from the tank to the unit cells and back to the tank occurs without the use of pumps or other such circulating devices, usually because of the above-noted production, at one or both of the electrodes, of gas bubbles which rise and tend to carry the electrolyte along with them. However, pumps are sometimes employed. In cases where the tank is positioned remote from the electrolytic cell rather than having the electrolytic cell in the tank, some form of pumping arrangement is necessary.

One of the disadvantages of the prior art electrolytic cells relates to the inlet and outlet tubes which provide communication between the housing and the tank. On the one hand, the inlet and outlet tubes must be large enough to permit good circulation of the electrolyte from the tank to the electrolyte cell when natural circulation is relied upon. On the other hand, the current flowing from one cell to an adjacent cell has some tendency to by-pass any given electrode by following a path through the electrolyte out of one cell through a communicating tube to the tank, through which it travels to another communicating tube for a cell further down, which it then enters. This problem, known as current leakage, becomes more and more acute whenever an attempt is made to promote electrolyte circulation by increasing the diameter of the inlet and outlet tubes and/ or decreasing their length.

Furthermore, the potential between the tank and an electrode in the electrolytic cell may be quite high, e.g., the end electrodes of the cell may be at +60 and 60 volts respectively, while the tank is at 0 volt. This diiierence in potential promotes current leakage, the degree of current leakage being greater as the difference in potential increases.

Another disadvantage in the prior art cells is related to control of the pH in the electrolyte. In the production of sodium chlorate by electrolysis it is necessary to add hydrochloric acid to the electrolyte in order to control pH. In the past, this has been done by adding HCl to the reaction zone, the major part of which is the volume of the tank occupied by the electrolyte, as opposed to the volume within the electrolytic cell. Relatively quiet pockets may be formed in the reaction zone of electrolytic apparatus of the aforementioned type, and because of lack of proper mixing, the addition of HCl may cause the pH of the solution in the pockets to fall quite low. This in turn may lead to the evolution of chlorine, which decreases the efliciency of the electrolytic process. Furthermore, the aforementioned pockets or dead zones decrease the eitective reaction zone volume.

It is an object of this invention to provide a bipolar electrode structure wherein, for a given electrolysis zone volume per unit lateral width of an electrode, the length of the electrolyte circulation path is reduced to a minimum, thereby maximizing the rate of circulation by reason of reducing to a minimum the frictional drag opposing electrolyte movement. The improved circulation of the electrolyte in the bipolar electrolytic cell according to this invention reduces or eliminates the occurrence of quiet pockets or dead spots in the reaction zones, such that the effective reaction zone volume can be virtually the whole of the available reaction zone volume. As well, chlorine evolution problems due to low pH in quiet pockets and the resultant decrease in efiiciency can be minimized or eliminated.

In addition to the above object, and in view of the above disadvantages of the prior art electrolytic cells, it is an object of a preferred embodiment of this invention to provide a bipolar electrolytic cell in which each electrolysis zone is associated with an in communication with a separate, individual reaction zone, thereby substantially reducing the problems associated with current leakage through a common reaction volume.

The above objects are attained through the provision,

for use in an electrolytic process which requires an electrolysis zone, and in which upward flow of the electrolyte is induced in the electrolysis zone due to the generation there of gas bubbles during the process, of a bipolar electrolytic cell having at least three electrodes arranged adjacent one another, at least one electrode being intermediate two other electrodes and being a bipolar electrode. Each bipolar electrode of the bipolar electrolytic cell comprises an anodic structure and a cathodic structure which are in electrically conductive communication with each other and which are constructed of suitable anodic and cathodic materials respectively. One of the structures has remote from the other structure a first portion adapted to be generally active electrolytically and to defined an electrolysis zone with the next adjacent electrode, and has a second portion proximate to the other structure. The first portion and the second portion are in electrically conductive communication with each other. The one structure referred to is provided with at least one substantially vertical channel intermediate said portions and generally encompassed by said one structure, the channel communicating at its upper end and at its lower end with the electrolysis zone adjacent said first portion such that the electrolyte induced to flow upwardly in the electrolysis zone due to the generation there of gas bubbles can flow back downwardly through the channel. Additionally, means are provided for protecting the inside surface of the channel against attack by the electrolyte.

According to one embodiment of this invention, the channel mentioned above is entirely enclosed within the said one structure except for the upper and lower ends thereof, and the means for protecting the inside surface of the channel against attack by the electrolyte comprises a lining on the inside surface of the channel, the lining being resistant to attack by the electrolyte.

Another particular embodiment of this invention is one wherein the cathodic structure is provided with the channel, and wherein the means for protecting the inside surface of the channel against attack by the electrolyte includes passage means communicating the channel with the electrolysis zone in a generally distributed manner over substantially the whole length of the channel, the passage means being such that when a voltage suitable for electrolysis is placed across the electrolysis zone there occurs between the next adjacent electrode and substantially the whole inside surface of the channel a limited electrical current sufficient to protect cathodically the inside surface against attack by the electrolyte but small enough to avoid the generation in the channel of gas bubbles at a rate which interferes substantially with electrolyte downflow in the channel.

Yet another embodiment of the invention is one in which the said one structure is the anodic structure, made of a material such as titanium or tantalum, either of which forms under anodic conditions an oxide impervious to attack by the electrolyte, the first portion being coated with a platinum metal on the surface adjacent the electrolysis zone, the means for protecting the inside surface of the channel against attack by the electrolyte including passage means communicating the channel with the electrolysis zone in a generally distributed manner over substantially the whole length of the channel, the passage means being such that when a voltage suitable for electrolysis is placed across the electrolysis zone there occurs between said next adjacent electrode and substantially the whole inside surface of the channel a limited electrical current sufficient to sustain on said inside surface the presence of a coating of the oxide of said metal, in order to protect said inside surface against attack by the electrolyte.

Further features and advantages of this invention will be apparent from the following detailed description, taken in conjunction with the appended drawings, in which like numerals refer to like parts throughout the several views, and in which:

FIGURE 1 is a partly broken-away perspective view of a bipolar electrode showing a first embodiment of this invention;

FIGURE 2 is a vertical sectional view of an electrolytic cell containing a plurality of electrodes of the kind shown in FIGURE 1, the section being taken transversely I to the electrodes;

FIGURE 3 is a perspective view of a bipolar electrode showing one construction'of a second embodiment of this invention;

FIGURE 4 is a perspective view of a bipolar electrode showing another construction of the second embodiment of this invention; and

FIGURE 5 is a perspective view of yet another construction of the second embodiment of this invention.

As used herein, the term bipolar electrolytic cell means an electrolytic cell in which at least one of the electrodes is bipolar, i.e., one face functions as an anode and the other face functions as a cathode, and in which, in use, each bipolar electrode is connected in series with two electrodes that bracket it. This is in contrast to a monopolar electrolytic cell in which all of the anodes are connected in parallel, and all of the cathodes are connected in parallel, electrical connection being made between each electrode and the positive or negative terminal of a rectifier.

Referring to FIGURE 2, a bipolar electrolytic 10 is constructed in the usual manner with a base 11, two parallel, spaced-apart end walls 12 upstanding at either end of the base 11 and two parallel side walls 13 (only one visible in FIG. 2) extending between and perpendicularly to the end walls 12 at right angles to the base 11. The bipolar electrolytic cell 10 is thus a box-like enclosure in the shape of a rectangular parallelepiped, although any other suitable shape could be employed. The bipolar electrolytic cell 10 contains a plurality of bipolar electrodes 14 arranged adjacent one another in spacedapart relation. Each bipolar electrode 14 includes two structures 15 and 16, one of which is the cathodic structure, and the other of which is the anodic structure. The following discussion assumes that the anodic structure is structure 15, but it will be apparent that structure 16 could also be the anodic structure.

The bipolar electrodes 14 are arranged within the cell such that the anodic structure 15 of one electrode is adjacent the cathodic structure 16 of the next electrode. One end wall 12 supports an end electrode 17 which functions anodically, while the other end wall 12 supports an end electrode 18 which functions cathodically. As shown, a DC power supply is connected across the end electrodes to supply the electrolytic cell 10 with electric current, and the cell 10 is filled with electrolyte to a level 18a.

Turning now to the electrode 14 shown in perspective in FIGURE 1, the anodic structure 15 and the cathodic structure 16 are shown directly bonded to each other. While it is preferred to bond the two structures 15 and 16 directly together, there is no reason why a further layer or layers could not be interposed between the structures 15 and 16, so long as the intervening layer or layers were electrically conductive and were capable of good conductive bonding to the structures 15 and 16.

As shown in FIGURE 1, the anodic structure 15 is a simple rectangular plate, and is preferably constructed of a valve metal such as titanium or tantalum which has a coating of a platinum metal applied to the active anodic surface. As is well known, the valve meatls titanium and tantalum have the characteristic of forming, under anodic conditions, their own oxide, which has a very high electrical resistivity and is substantially impervious to attack by the electrolyte, thus protecting the underlying tantalum or titanium as the case may be. Due to its high resistivity, however, the oxide of the valve metal cannot function anodically, and for this reason a thin layer of a platinum-type metal is coated on the unoxidized metal. The term platinum-type metal is here intended to include: platinum, ruthenium, rhodium, palladium osmium, iridium, and alloys of two or more of these metals. The cost of platinum-type metals is high, and for this reason only a very thin layer of the platinumtype metal is normally used to coat the tantalum or titanium. Because pinholes and other irregularities are often present in the thin metal layer, the electrolyte often penetrates through this layer to the underlying tantalum and titanium which, were it not for the formation of their oxide, would be attacked by the electrolyte in such a way as to strip off the platinum-type metal layer.

Many materials used in electrolytic cells (iron, copper, etc.) are violently attacked by the electrolyte under anodic conditions, and would prove unsuitable as an anode in the present situation. However, when in the appended claims the term suitable anodic material is employed, it is intended to include the preferred construction of tantalum or titanium with a platinum-type metal layer, and any other material or combination of materials which would function satisfactorily as an anode.

The cathodic structure 16 is seen in FIGURE 1 to consist basically of two portions: a first portion 19 remote from the other structure and adapted to be generally active electrolytically, and a second portion proximate to the other structure 15. As shown in FIG- URE 2, the first portion 19 is situated closely adjacent, but spaced from, the anodic structure 15 of the next electrode and defines therewith an electrolysis zone 21 of small transverse dimension. The first portion 19 and the second portion 20 are in electrically conductive communication with each other through the spacer walls 22 extending therebetween. Preferably, the entire cathodic structure 16 is of integral construction. As can be seen, the'first portion 19 and the second portion 20 are in the-form of flat plates spaced in parallel relationship by the spacer walls 22.

Defined between the first portion 19 and the second portion 20 and intermediate the spacer walls 22 are three substantially vertical channels 23 which communicate at their upper ends and at their lower ends with the electrolysis zone 21 defined between the first portion 19 and the anode 15 of the next electrode. Although three channels 23 are shown in FIGURE 1, any number of channels may be provided, including a single channel. What is essential is that the channel or channels be oriented substantially vertically, for a reason later to be explained.

Because of the relative proximity of the first portion 19 of one electrode to the structure 15 of the adjacent electrode, the resistance to current flow offered by the electrolyte is the least in the electrolysis zone 21 defined therebetween. For this reason, most of the current flow between the two electrodes will take place in the electrolysis zone 21, and practically all of the electrolysis of the electrolyte will take place there as well. The distance between the second portion 20 and the anodic structure 15 of the adjacent electrode is much greater than the transverse dimension of the electrolysis zone 21, and only a very weak current is induced to flow'through the electrolyte to the area 24, which is the submerged surface of the portion 20 which is above the channels 23. For this reason, very little electrolysis will take place at the area 24. Although a much reduced current flows to the area 24 of the second portion 20, it is sufficient to protect it cathodically against attack by the electrolyte. As for points centrally within the interior of the channels 23, however, the electrolyte path linking them to the anodic structure 15 of the adjacent electrode is considerably longer even than the path from the area 24 to the anodic structure 15, and the resistance to current fiow is too high to permit sufiicient current flow for cathodic protection. For this reason, some means for protecting the inside surface of the channel 23 against attack by the electrolyte must be provided.

One way of protecting the inside surface of the channels 23 against attack by the electrolyte is to coat the inside surface thereof with a lining of a material resistant to attack by the electrolyte. Glass, for example, would provide a satisfactory lining, and there are several plastic materials, well known to those familiar with the art, which could be employed as well.

The cathodic structure 16 should be made of a suitable cathodic material. By suitable cathodic material is meant a material which is electrically conductive, substantially insoluble in the electrolyte under cathodic conditions, resistant to reduction, and either substantially impermeable Wih respect to H or if permeable by H substantially dimensionally stable with respect to H Steel is the preferred material, but it would also be pos sible to use copper, chromium, cobalt, nickel, lead, tin, iron, molybdenum, tungsten, or alloys of the above metals. Graphite or lead dioxide might also be used. If the cathodic material is permeable with respect to H it is preferable that any layer or layers intermediate the anodic and cathodic structures be either impermeable with respect to H or if permeable by H substantially dimensionally stable with respect to H It also might be possible to employ titanium or tantalum as a cathodic material, but these: have been known to suffer from lack of dimensional stability with respect to H As well, their electrical conductivity is low compared to iron.

The electrolyte circulation characteristics between two adjacent electrodes are as follows. The production of small gas bubbles, particularly of H at the active cathode surface of the first portion 19 (i.e., within the electrolysis zone 21) tends to cause the electrolyte in the electrolysis zone 21 to rise. The channels 23 provide downfiow passages for the electrolyte, such that a closed circuit can be set up with the electrolyte flowing upwardly in the electrolysis zone 21 and downwardly in the channels 23, as represented by the arrows in FIG- URE 1.

The structure 16 could be the anodic structure instead of the cathodic structure. With such a construction, the preferred material for the anodic structure is either titanium or tantalum, with a coating of a platinum-type metal on the electrolytically active surface of the portion 19. All parts of the surface of structure 16 which are not coated with a layer of a platinum-type metal will, under anodic conditions, generate a layer of the oxide of the metal, which will protect the unplatinized surface against attack. In the anodic situation, it is likely that even at the central areas on the inside of the channels 23 there will be sufiicient electrical current to generate a protective oxide layer. If not, a suitable inert layer such as glass can be employed, as before.

Three examples of a second embodiment of this invention are shown in FIGURES 3, 4 and 5. In the second embodiment, instead of using a layer or lining 25 to protect the inside surface of the channels 23, passage means is provided in the first portion 19 to communicate the channels 23 with the electrolysis zone in a generally distributed manner over substantially the whole length of the channels 23. In FIGURE 3, the passage means is shown as a plurality of circular holes 26 through the portion 19, whereas in FIGURE 4 the passage means takes the form of elongated vertical slots located centrally with respect to each channel 23. When a voltage suitable for electrolysis is placed across the electrolysis zone between two adjacent electrodes, there occurs between the next adjacent anode and substantially the whole inside surface of each channel a limited electrical current which interacts with the inside surface to protect the latter against attack by the electroltye.

In the case where the cathodic structure 16 is the cathode, the passage means is of a size such as to permit flow of electrical current sufiicient to protect cathodically the inside surface of the channels 23 against attack by the electrolyte, but small enough to avoid the generation in the channels 23 of gas bubbles at a rate which interferes substantially with electrolyte downflow in the channels 23. It is likely that some generation of gas bubbles in the channels 23 cannot be avoided, since some current does flow to the inside surface thereof. However, if this current is kept to a minimum, the gas bubbles are not generated at a sufficient rate to significantly oppose downfiow of the electrolyte in the channels 23.

Where the structure 16 is the anode, the passage means permits the flow of an oxide-forming current to the inside surface of the channels 23, thereby ensuring the protection of the latter against electrolyte attack.

Naturally, the passage means need not take the particular form of either circular holes or elongated slots as shown in FIGURES 3 and 4, but can be in any suitable form which permits a current flow meeting the above conditions.

It will be realized that a particular advantage of the second embodiment shown in FIGURES 3 and 4 is that it is unnecessary to provide a special lining or covering for the inside surface of channels 23, as these are now either cathodically protected, or covered by a protecting oxide, depending on whether the cathodic structure or the anodic structure contains the channels 23.

When the structure 16 in FIGURES 3 and 4 is the cathodic structure, the same materials may be used as were listed in connection with the FIGURE 1 embodiment.

The advantages of this invention with regard to electrolyte circulation can be seen from FIGURES 1 and 2. In the first place, voltage considerations make it necessary that the electrolysis zone 21 have a very small transverse dimension with respect to its breadth and height. For economic operation, the width of the electrolysis zone 21 should be in the neighbourhood of /s%. Because of the high ratio of surface area to volume for the electrolysis zone, a considerable frictional drag is exerted on the upwardly moving electrolyte. There is little that can be done about this situation, because the width of the zone must of necessity be small. This invention, however, by providing reaction channels 23 immediately adjacent the electrolysis zone in the transverse direction, such that the general plane of electrolyte circulation is perpendicular to the major dimensions of the electrolysis zone, creates the shortest possible electrolyte path for a given electrolysis zone volume per unit breadth of the electrode. It will be readily appreciated that if, instead of being located within the cathodic structure itself, the reaction zones or channels were positioned laterally to the left or to the right of the electrolysis zone, such that the general plane of electrolyte circulation were parallel to the major dimensions of the electrolysis zone, the mean electrolyte circulation path could not help but be considerably greater than the path in the present invention.

An additional advantage of the construction of this invention, particularly in the FIGURE 1 embodiment, is related to the fact that there are no characteristics of the electrolytic process that place a maximum limit on the transverse dimension of the channels 23, so that the latter dimension can be increased in-order to reduce the ratio of surface area per unit volume of a channel, thereby reducing the effect of frictional drag on electrolyte moving downwardly therein.

Some limitation of the transverse dimension of the channels 23 is introduced in the embodiment shown in FIGURES 3 and 4, by the fact that the transverse dimension of the channels must not be so great that the current flowing to the second portion 20 is insufficient to protect the latter cathodically. However, since all of the factors of voltage, transverse dimension of the channels 23, and the size of the passage means 26 and 27 are interrelated and can be made to compensate for one another, the problem of a current limitation on the maximum transverse dimension of the channels 23 will not be serious.

The electrode shown in FIGURE 4 is a preferred embodiment from the point of view of ease of construction. It is made up of separate plate-like members welded together at the appropriate points. Assuming that the structure 16 is the cathodic structure and that it is made of iron, a simple rectangular iron plate 29 constitutes the second portion 20, and is bonded by a suitable process such as cladding to the anodic structure 15, the latter being, e.g., platinized titanium. A plurality of elongated iron plates or bars 30 are then vertically welded edgewise to the rectangular iron plates at points spaced evenly across the latter. Following this, a plurality of cross-bars or T-bars 31 are welded centrally to the bars 30 to form therewith vertically elongated protuberances of generally T-shaped horizontal section extending outwardly from the flat plate 29. Alternatively, integral rolled T-sections could be used instead of the bars 30 and 31. The crossbars of the T-shapes constitute the first portion 19 mentioned above, and they are separated or spaced apart to provide the elongated slots 27 which constitute the passage means, each pair of adjacent T-shaped protuberances defining therebetween a channel 23.

Another preferred embodiment is that shown in FIG- URE 5. A plate 33 of iron is bonded to a plate 34 of titanium. Projecting at right-angles from the titanium plate 34, and welded thereto, is a plurality of cylindrical titanium rods 35. A second titanium plate 37 is attached to the ends of the rods 35 by titanium screws 38 and is coated with platinum on the face remote from the plate 34 (preferably by platinization). Apertures 39 are provided at spaced locations over the face of the plate 37, and may be of any appropriate shape and size, consistent with the necessity of maintaining a layer of titanium oxide on the surface of the plate 34, on the rods 35 and on the far side (unplatinized) of the plate 37.

Naturally there is no reason why both of the structures making up a single electrode could not be provided with the vertical channels 23 to constitute reaction zone :downfiow channels for the electrolyte.

The compound bipolar electrolytic cell according to this invention can be used for both batch operation and cascade operation. When used for batch operation, the individual inter-electrode spaces are completely isolated from one another, and each inter-electrode space is provided with an inlet tube (or tubes) and an outlet tube (or tubes) for, respectively, charging the inter-electrode space with electrolyte and removing the electrolyte therefrom. When the inter-electrode spaces are cascaded, apertures or tubes through the electrodes are provided to interconnect adjacent inter-electrode spaces, and to permit passage of the electrolyte from one to another. For cascade operation, it is advisable that the apertures or tubes be positioned so as not to be directly in the path of electrolyte circulation between the electrolysis zone and the :downflow channels. A suitable location for the tubes or apertures would be the area 40 near the bottom edge of the electrode.

Where this invention is practised with electrolytic processes that require a reaction zone, it is preferred that the total reaction zone for each individual electrolysis zone be constituted by the respective downfiow channel or channels communicating with the particular electrolysis zone. It would also be possible, however, to provide a plurality of laterally located, separate, auxiliary reaction zones, each communicating with a separate one of the inter-electrode spaces, although such an arrangement would lengthen the mean electrolyte circulation path and consequently diminish the advantages attendant upon the above preferred arrangement. An even less desirable, but nonetheless possible, arrangement would be one in which the electrolytic cell were partially immersed in a reaction tank, tubes being provided to communicate each interelectrode space with the common volume of electrolyte in the tank. The main disadvantage of the latter arrangement would be the problem or current leakage through the common tank volume from one inter-electrode space to another, as discussed at the beginning of this disclosure with respect to the prior art graphite cells.

While a preferred embodiment of this invention has been disclosed herein, those skilled in the art will appreciate that changes and modifications maybe made therein without departing from the spirit and scope of this invention as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. For use in an electrolytic process which requires an electrolysis zone, and in which upward flow of the electrolyte is induced in the electrolysis zone due to the generation there of gas bubbles during the process, a bipolar electrolytic cell having at least three electrodes arrangedadjacent one another, at least one electrode being intermediate two other electrodes and being a bipolar electrode comprising:

an anodic structure and a cathodic structure, the

structures being in electrically conductive communication with each other and being construced of suitable anodic and cathodic materials respectively,

one structure having remote from the other structure a first portion adapted to be generally active electrolytically and to define an electrolysis zone with the next adjacent electrode, and having a second portion proximate to the other structure, said portions being in electrically conductive communication with each other,

said one structure being provided with at least one substantially vertical channel intermediate said portions and generally encompassed by said one structure, said channel communicating at its upper end and at its lower end with the electrolysis zone adjacent said first portion such that the electrolyte induced to flow upwardly in said electrolysis zone due to the generation there of gas bubbles can flow back downwardyl through said channel,

and means for protecting the inside surface of said channel against attack by the electrolyte.

2. A bipolar electrolytic cell as claimed in claim 1 in which the channel is entirely enclosed Within the said one structure except for said upper and lower ends, and in which said means comprises a lining on the inside surface of said channel, said lining being resistant to attack by the electrolyte.

3. A bipolar electrolytic cell as claimed in claim 2 in which said one structure is the cathodic structure constructed of a material chosen from among: iron, steel, copper; and in which the lining is made of material chosen from among: plastic, glass, titanium, tantalum.

4. A bipolar electrolytic cell as claimed in claim 2 in which said structure is the anodic structure constructed of a material chosen from among: titanium, tantalum; in which the lining is the oxide of the anodic material; and in which the said first portion is coated with a platinum-type metal on the surface adjacent the electrolysis zone.

5. A bipolar electrolytic cell as claimed in claim 1 in whichthe two structures are directly bonded to each other, and in which said one structure is of integral construction.

6. A bipolar electrolytic cell as claimed in claim 1 in which said means comprises passage means provided in said first portion to communicate said channel with said electrolysis zone in a generally distributed manner over substantially the whole length of said channel, the passage means being such that when a voltage suitable for electrolysis is placed across the electrolysis zone there occurs between said next adjacent electrode and substantially the whole inside surface of said channel, a limited electrical current which interacts with said inside surface to protect the latter against attack by the electrolyte.

7. A bipolar elecrolytic cell as claimed in claim 1 in which said one structure is the cathodic structure, and in which said means comprises passage means provided in said first portion to communicate said channel with said electrolysis zone in a generally distributed manner over substantially the Whole length of said channel, the passage means being such that when a voltage suitable for electrolysis is placed across the electrolysis zone there occurs between said next adjacent electrode and substantially the whole inside surface of said channel a limited electrical current sufiicient to protect cathodically said inside surface against attack by the electrolyte but small enough to avoid the generation in the channel of gas bubbles at a rate which interferes substantially with electrolyte downflow in the channel.

8. A bipolar electrolytic cell as claimed in claim 1 in which said one structure is the anodic structure, the anodic structure being constructed of a material chosen from among: titanium, tantalum; the said first portion being coated with a platinum-type metal on the surface adjacent the electrolysis zone; and in which said means comprises passage means provided in. said first portion to communicate said channel with said electrolysis zone in a generally distributed manner over substantially the Whole length of said channel, the passage means being such that when a voltage suitable for electrolysis is placed across the electrolysis zone there occurs between said next adjacent electrode and substantially the whole inside surface of said channel, a limited electrical current sufiicient to sustain on said inside surface the presence of a coating of the oxide of said material, to protect said inside surface against attack by the electrolyte.

9. A bipolar electrolytic cell as claimed in claim 6 in which said passage means comprises an elongated slot running substantially the whole length of the channel.

10. A bipolar electrolytic cell as claimed in claim 6 in which said passage means comprises a plurality of apertures spaced along the length of the channel.

11. A bipolar electrolytic cell as claimed in claim 7 in which the cathodic structure comprises a flat plate constituting said second portion, said flat plate being bonded directly to said anodic structure, and a plurality of vertically elongated protuberances of generally T-shaped horizontal section extending from said fiat plate, the crossbars of the T-shapes constituting said first portion, the elongated protuberances being spaced to provide elongated slots between the cross-bars of the T-shapes, each pair of adjacent protuberances defining a channel, said slots constituting said passage means.

References Cited UNITED STATES PATENTS 1,001,876 8/1911 McDorman 204-268 3,055,821 9/1962 Holmes et al 204-290 3,269,932 8/ 1966 Worsham et al. 204-270 JOHN H. MACK, Primary Examiner. D. R. JORDAN, Assistant Examiner.

US. Cl. X.R. 204-237, 269, 290 

1. FOR USE IN AN ELECTROLYTIC PROCESS WHICH REQUIRES AN ELECTROLYSIS ZONE, AND IN WHICH UPWARD FLOW OOF THE ELECTROLYTE IS INDUCED IN THE ELECTROLYSIS ZONE DUE TO THE GENERATION THERE OF GAS BUBBLES DURING THE PROCESS, A BIPOLAR ELECTROLYTIC CELL HAVING AT LEAST THREE ELECTRODES ARRANGED ADJACENT ONE ANOTHER, AT LEAST ONE ELECTODE BEING INTERMEDIATE TWO OTHER ELECTRODES AND BEING A BIPOLAR ELECTRODE COMPRISING: AN ANODIC STRUCTURE AND A CATHODIC STRUCTURE, THE STRUCTRUES BEING IN ELECTRICALLY CONDUCTIVE COMMUNICATION WITH EACH OTHER AND BEING CONSTRUCTED OF SUITABLE ANODIC AND CATHODIC MATERIALS RESPECTIVELY, ONE STRUCTURE HAVING REMOTE FROM THE OTHER STRUCTURE A FIRST PORTION ADAPTED TO BE GENERALLY ACTIVE ELECTROLYTICALLY AND TO DEFINE AN ELECTROLYSIS ZONE WITH THE NEXT ADJACENT ELECTRODE, AND HAVING A SECONG PORTION PROXIMATE TO THE OTHER STRUCTURE, SAID PORTIONS BEING IN ELECTRICALLY CONDUCTIVE COMMUNICATION WITH EACH OTHER, SAID ONE STRUCTURE BEING PROVIDED WITH AT LEAST ONE SUBSTANTIALLY VERTICAL CHANNEL INTERMEDIATE SAID PORTIONS AND GENERALLY ENCOMPASSED BY SAID ONE STRUCTURE, SAID CHANNEL COMMUNICATING AT ITS UPPER END AND AT ITS LOWER END WITH THE ELECTROLYSIS ZONE ADJACENT SAID FIRST PORTION SUCH THAT THE ELECTROLYTE INDUCED TO FLOW UPWARDLY IN SAID ELECTROLYSIS ZONE DUE TO THE GENERATION THERE OF GAS BUBBLES CAN FLOW BACK DOWNWARDLY THROUGH SAID CHANNEL, AND MEANS FOR PROTECTING THE INSIDE SURFACE OF SAID CHANNEL AGAINST ATTACK BY THE ELECTROLYTE. 